Field of the Invention
The present invention generally relates to a vehicle adaptive steering control apparatus. More specifically, the present invention relates to an adaptive steering control apparatus that continuously independently adjusts the steering angle of each of the steerable wheels of a vehicle.
Background Information
The text FUNDAMENTALS OF VEHICLE DYNAMICS by Thomas D. Gillespie (hereinafter the “Gillespie text”) describes various steering assemblies and the geometry that is used to configure and design such steering assemblies. For example, the Gillespie text describes rack and pinion steering linkages, steering gearbox linkages and truck steering systems and the basic geometry used to design each system. The fundamentals set forth in the Gillespie text are hereinafter referred to as “Ackermann steering geometry”. Ackermann steering geometry balances a number of inter-related issues and is typically employed in systems where steerable wheels in the vehicle (usually the front wheels) are mechanically linked together such that the steerable wheels are moved together simultaneously during turning and steering movements. Ackermann steering geometry assumes that when the vehicle is moving approximately in a straight trajectory, the steerable wheels are provided what is referred to as “toe-in” angles, where the two front tires are not absolutely parallel to one another at a stop, but are angled slight toward one another aiming at a point far ahead of the vehicle. The “toe-in” angle is provided because at highway speeds, the forces acting on the front wheels tends to push forward portions of the vehicle away from one another. The “toe-in” angle compensates for the outward movement of the front wheels. During turning operations, a toe angle (relative turning radius between two steerable wheels) continually changes, depending upon the overall degree of the turn of the vehicle, as is explained in the Gillespie text.
Consequently, the Ackermann steering geometry based steering system is configured such that during a right turn, the right front wheel is turned to the right with a greater angular displacement than the left front wheel. Similarly, during a left turn, the left front wheel is turned to the left with greater angular displacement than the right front wheel.
Ackerman steering geometry based steering systems do not necessarily take into account additional forces acting on the steerable wheels during a turning operation. For example, during a cornering operation, forces (for example, centrifugal forces) acting on the outboard wheel (the left wheel in a right turn, the right wheel in a left turn) differ from the forces acting on the inboard wheel (the left wheel in a left turn, the right wheel in a right turn). Conventional Ackermann steering geometry based steering mechanisms have no means for making adjustments in the movements of the steerable wheels in response to increased forces acting on the steerable wheels during a turning operation.